There is a desired for coloured solid detergent products, unfortunately it is found that such products can give rise to unacceptable coloured staining.
WO9932599 describes a method of manufacturing laundry detergent particles, being an extrusion method in which a builder and surfactant, the latter comprising as a major component a sulphated or sulphonated anionic surfactant, are fed into an extruder, mechanically worked at a temperature of at least 40° C., preferably at least 60° C., and extruded through an extrusion head having a multiplicity of extrusion apertures. In most examples, the surfactant is fed to the extruder along with builder in a weight ratio of more than 1 part builder to 2 parts surfactant. The extrudate apparently required further drying. In Example 6, PAS paste was dried and extruded. Such PAS noodles are well known in the prior art. The noodles are typically cylindrical in shape and their length exceeds their diameter, as described in example 2.
U.S. Pat. No. 7,022,660 discloses a process for the preparation of a detergent particle having a coating.
WO 2010/122051 discloses coated detergent particles and a dye.
EP 2166 077 discloses particles comprising a core and a dye.
Pigments are coloured particles, which are practically insoluble in aqueous medium that contain surfactants. Pigments have zeta potential because they are suspended in the liquid medium containing surfactant unlike dyes which are soluble therein.